High-contrast room-light-handleable black-and-white silver halide photographic elements are well known and widely used in graphic arts applications. The term "room-light-handleable" is intended to denote that the material can be exposed to a light level of 200 lux for several minutes without a significant loss in performance.
The silver halide emulsions utilized in high-contrast room-light-handleable photographic elements are slow speed emulsions, with the desired slow speed typically being achieved by the use of small grain sizes and by the doping of the silver halide grains with appropriate doping agents that control photographic speed. The incorporation of filter dyes in an overcoat layer of the photographic element to absorb unwanted light and decrease photographic speed is also a commonly employed technique.
The high-contrast room-light-handleable photographic elements that are in widespread use typically employ silver halide grains that are of small size; the term "small size" being used herein to mean a mean grain size in the range of from 0.14 to 0.4 micrometers. Certain advantages can be obtained by using silver halide grains of very small size; the term "very small size" being used herein to mean a mean grain size of less than 0.12 micrometers. Thus, for example, the use of very small size silver halide grains provides an improvement in safelight handling characteristics, permits the use of less silver and reduces the need to use filter dyes.
While high-contrast room-light-handleable photographic elements utilizing very small size silver halide grains have many advantages, as indicated above, they are lacking in certain desirable features, for example, they do not exhibit an adequate degree of print-out image upon exposure. To facilitate handling, it is advantageous that the photographic element print out an image, even though it is only faintly visible, upon normal exposure. Such a print-out image is readily obtained with silver halide grains of small size but not with silver halide grains of very small size, as those terms are used herein. Thus, for example, utilizing a silver halide emulsion layer with grains having a mean grain size of 0.16 micrometers will give a print-out image with an acceptable degree of visibility upon normal exposure but utilizing a silver halide emulsion layer with grains of the same halide content and content of doping agent but a mean grain size of 0.08 micrometers will not.
High-contrast room-light-handleable black-and-white photographic elements known heretofore have been lacking in one or more desirable features and this has hindered their commercial utilization. In particular, they have typically required a relatively high silver coverage and the use of expensive filter dyes and both of these features have added significantly to the cost of these products. Examples of patents describing such photographic elements include Takahashi et al, U.S. Pat. No. 3,818,659, issued Apr. 4, 1989; Miyata et al, U.S. Pat. No. 4,847,180, issued Jul. 11, 1989; Gingello et al, U.S. Pat. No. 5,061,595, issued Oct. 29, 1991; Kameoka et al, U.S. Pat. No. 5,085,970, issued Feb. 4, 1992; and Gingello et al, U.S. Pat. No. 5,175,073, issued Dec. 29, 1992.
U.S. Pat. No. 5,279,933 describes a high-contrast room-light-handleable black-and-white silver halide photographic element that is able to print out a visible image on normal exposure. This element is comprised of a support, an imaging layer containing doped silver halide grains with a mean grain size of less than 0.12 micrometers, and a print-out layer containing doped silver halide grains with a mean grain size of from 0.14 to 0.4 micrometers. The dopant level in the silver halide grains is controlled so that the photographic speed of the imaging layer is higher than the photographic speed of the print-out layer even though the grains of the imaging layer are smaller than the grains of the print-out layer.
While the high-contrast room-light-handleable photographic elements of U.S. Pat. No. 5,279,933 represent a major advance in the art, they would benefit from still further improvement in their properties especially in regard to safelight handling characteristics. It is toward the objective of providing such further improvement that the present invention is directed.